Sweeping up the banknotes from the street after the Hungarian pengő was replaced in 1946.

In 1956, Phillip Cagan wrote The Monetary Dynamics of Hyperinflation, the book often regarded as the first serious study of hyperinflation and its effects[4] (though The Economics of Inflation by C. Bresciani-Turroni on the German hyperinflation was published in Italian in 1931[5]). In his book, Cagan defined a hyperinflationary episode as starting in the month that the monthly inflation rate exceeds 50%, and as ending when the monthly inflation rate drops below 50% and stays that way for at least a year.[6] Economists usually follow Cagan’s description that hyperinflation occurs when the monthly inflation rate exceeds 50%.[4]